WLAN Standards

Typically, government agencies control the use of RF bands. For example, in   the United States, the Federal Communications Commission (FCC) regulates wireless transmissions, which includes new transmission methods, frequencies, and  modulations; in Europe, the European Telecommunications Standards Institute   (ETSI) is the regulator. However, one international agency, the International  Telecommunication Union-Radio Communication Sector (ITU-R) is responsible  for managing the radio frequency (RF) spectrum and satellite orbits for wireless   communications: its main purpose is to provide for cooperation and coexistence of   standards and implementations across country boundaries.

Two standards bodies are primarily responsible for implementing WLANs: the Institute of Electrical and Electronic Engineers (IEEE) and the Wi-Fi Alliance. IEEE defines the mechanical process of how WLANs are implemented in the 802.11 standards so that vendors can create compatible products. The Wi-Fi Alliance basically certifies companies by ensuring that their products follow the 802.11 standards, thus allowing customers to buy WLAN products from different vendors without having to be concerned about any compatibility issues. Cisco is a founding member of the Wi-Fi Alliance. You can find a list of certified vendor products at www.wi-fi.com.

RF Bands

 Wireless communications can use various RF bands. Some of these are licensed (you have to pay a governmental agency to use them) and some are unlicensed. For example, radio broadcasts, such as AM and FM, are licensed through your country’s government. Other bands, such as the 802.11 bands, are unlicensed, so you don’t have to buy a license from the government to use these frequencies. However, unlicensed bands are still regulated by governments, which might define restrictions in their usage. WLANs use three unlicensed bands:

■   900 MHz Used by older cordless phones

■   2.4 GHz Used by newer cordless phones, WLANs, Bluetooth, microwaves,  and other devices

■   5 GHz Used by the newest models of cordless phones and WLAN devices

A hertz (Hz) is a unit of frequency that measures the change in a state or cycle  in a wave (sound or radio) or alternating current (electricity) during 1 second. A megahertz (MHz) is 1 million cycles per second and a gigahertz (GHz) is 1 billion   cycles per second. The word hertz is from Heinrich Hertz, a German physicist who  first discovered that you could send and receive waves through the air.

The 900 MHz and 2.4 GHz frequencies are commonly referred to as the Industrial, Scientific, and Medical (ISM) bands and the 5 GHz frequency the Unlicensed National Information Infrastructure (UNII) band.

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